This invention relates to an improved method and apparatus for the manufacture of metal cans, and more particularly to improved method and apparatus for necking the open end of a metal can.
Metal cans may be formed in a variety of ways. A common method of forming metal can bodies is by the drawing and ironing process which produces a seamless can body having only one open end. These can bodies are most desirably provided at their open end with a necked-in portion and flange so that their open ends can be sealed by a can top with double seams that do not project outwardly of the can body. In such a can, the external diameter of the can top, including its double seam attachment, is about equal to the external diameter of the can body.
Methods and apparatus for necking-in and flanging can bodies are well known in the art. Included among prior patents relating to necker-flangers and their operation are U.S. Pat. Nos. 3,688,538; 3,754,424; 3,765,351; 3,872,314; 3,782,315; 3,874,209; 3,967,488; 4,070,888; and 4,176,536.
In addition to the methods and apparatus disclosed in the above patents, the open ends of can bodies have been provided with a neck of reduced diameter by the necker-flanger of the Reynolds Aluminum Company which carries their designation NC-8B (shown in FIG. 1). This necking tool has a stationary outer base and reciprocating concentric die and pilot assemblies that are movable longitudinally within the outer base. The reciprocating die member, which is arranged between the outer base and the pilot assembly, carries the necking die surface and is positively driven, for example, by a cam engaging its rear surface. The reciprocating pilot assembly is spring-loaded forwardly from the reciprocating die member. The forward portions of the die member and pilot assembly are intended to enter the open end of the can body and to form the neck of the can.
In operation, a can body to be provided with a neck is positioned opposite the necking tool with the bottom of the can body resting against a supporting surface. The die member is driven forwardly and, through its spring-loaded interconnection with the pilot assembly, drives the pilot assembly forwardly from the stationary base toward the open end of the can. The outer end of the pilot assembly enters the open end of the can in advance of the die member to provide an anvil surface against which the die can work. The forward advance of the pilot assembly is stopped, by the engagement of a homing surface on the stationary base with an outwardly projecting rear portion of the pilot assembly, slightly before the forward portion of the die member engages the open end of the can. As the die member continues to be driven forwardly by the cam, its die-forming surface deforms the open end of the can against the anvil surface of the pilot assembly to provide a necked-in end to the can body.
Upon completion of the formation of the necked-in open end, the reciprocating die member and pilot assembly are driven rearwardly within the stationary base. The metal can body is held stationary against its supporting surface by the application of compressed air from the necking tool. The pilot assembly is provided with a central passageway which is connected with a source of compressed air. Prior to the rearward movement of the die-forming member, air pressure is supplied to the interior of the can body through the central passageway formed in the pilot assembly. The air pressure provides a force on the bottom of the can, tending to move it away from the necking tool, and holds the bottom of the metal can body against its supporting surface as the die and pilot are moved rearwardly. The compressed air is turned off as the pilot assembly clears the open end of the can.
In normal operation, the pilot assembly remains stationary during the first part of this motion because it is spring-loaded forwardly and its outwardly projecting rear portion remains engaged with the homing surface of the stationary base. With the continued rearward movement of the outer die member, the die member at its rear contacts the projecting rear portion of the pilot assembly so that both are driven rearwardly and disengage the open end of the can. When the die member and pilot assembly have completed their rearward movement into the stationary base, the can is free to move to its next stage of formation.
In the above methods and apparatus, however, because of variations in the thickness of metal at the open end of the can and other variations in the prior manufacturing steps, the open end of the can frequently becomes jammed between the closely fitting and concentric die-forming surface of the die member and the interior anvil surface of the pilot assembly. In such situations, the force applied by the spring tending to urge the pilot assembly forwardly from the die member and the force of the ir pressure are not sufficient to overcome the resulting frictional engagement of the die member, the can body, and the pilot assembly. Thus, the die member, the can body, and the pilot assembly become jammed together, and as the die member is driven backwardly by the cam, the pilot assembly and can body also are moved backwardly together, and the air pressure in the can cannot eject the can body from the necking tool. This results in the can body being moved into such an improper position with respect to the remainder of the can-handling system that it is torn apart by other can-handling parts of the system, such as the discharge rails, and a portion of the can body remains in the space between the die member and the pilot assembly, blocking the entry of other can bodies and rendering the necking tool inoperable. In these situations, it is necessary to stop manufacturing, disassemble the necking tool from the machine, and remove from between the pilot assembly and die member the remains of the torn can body. In addition, sometimes the discharge rails and other portions of the machine are damaged and need repair. In the past, stoppages of this kind were frequent, happening as many as several times an hour. Each such stoppage took five to ten minutes to clear.
Such stoppages represent a significant loss of production. Cans are manufactured at very high rates, and can operations like the necking operation occur at a rate up to 1400 cans per minute. Thus, such stoppages represent a loss on the order of 5000 to 10,000 cans per hour of production, and an annual loss of as much as 50,000,000 cans. This significant loss of production was solved with the invention of this application.